MQTT

MQTT is the universal control channel between Hannah Core and satellites — the one channel that reaches both directly UDP-connected satellites and proxy-connected ones, which is why every control command (not audio) goes through it rather than UDP.

Key topics

Topic	Purpose
hannah/server (retained)	Discovery: proxy host:port
hannah/announce, hannah/announceSSML	External → Core: room announcement
hannah/notification	External → Core: system notification
hannah/volume (+ /state)	Global volume set/read
hannah/satellite/{device}/volume/set (+ /state)	Per-satellite volume
hannah/satellite/{device}/mute/set (+ /state)	Per-satellite mute
hannah/satellite/{device}/dnd (+ /state)	Do-not-disturb
hannah/satellite/{device}/listen	Core → satellite: enable virtual push-to-talk (e.g. after a follow-up question)
hannah/satellite/{device}/play_asset	Core → satellite: play a sound asset
hannah/satellite/{device}/ota/pending / /ok	OTA update request / approval
hannah/satellite/{device}/firmware	Satellite → Core: current firmware version
hannah/satellite/{device}/sensors	Satellite → Core: environmental sensor readings